to imagine unless you or a loved one have experienced it. A diagnosis of cancer. In daniel biljanoski's case an aggressive brain cancer untreatable at most hospitals. The prognosis is dreary. Perhaps a year to live. But for daniel and his family especially devastating. He was just 12 years old. His very first day at st. Jude's children's research hospital in memphis, "nightline" was there to witness a rigorous, groundbreaking treatment and one very courageous young man. When daniel and his mother, lisa, arrive at st. Jude -- please come to the ctu. Reporter: -- It is an act of both hope and desperation. I'm sure he's exhausted. Hit the pillow at -- Reporter: Doctors at his home in upstate new york have told his parents they think he has less than a year to live. Tell me about that moment when they look at you and say your baby -- it's terrible. It's horrible. Let me put this on your arm. Reporter: One set of worries is quickly removed. You know everything here is paid for through st. Jude. You'll never get a bill from st. Jude for anything. Reporter: And for daniel it may also be a last hope. We're going to go get some vital signs. Reporter: The type of brain cancer he has, atrt, is untreatable at most hospitals. But for more than a decade dr. Ahmad gajar here at st. Jude has been pioneering a new treatment which he believes may save daniel's life. Is the tumor he has amongst the worst you've seen in children? It is an aggressive tumor in children. No question about it. Reporter: The treatment will be grueling. Be careful about -- Reporter: Daniel may well lose some of his hearing and some of his strength. His ability to learn may also be affected. The question is how much? So before daniel begins treatment, everything is measured. There's a chance that there will make you sick to your stomach, the radiation. Reporter: Attacking the cancer with a treatment so aggressive that children under 3 cannot survive it without suffering significant brain damage. That's the brain tumor? That's it. Reporter: Dr. Thomas merchant is also part of the team. All of this is the tumor? Right. This little boy had a tumor that consumed almost a quarter of his brain. It was very extensive. I'll be here for quite some time, but just knowing the doctors and everyone is so nice, you know that you're in great care. Reporter: With all the support and kindness, this is still a hospital. If you could have a brain surgery you could get -- Reporter: These are still children, children with cancer, who must endure poking and prodding and needles. All right. That's it. You know where the toy chest is. You get to get something out of the toy chest. Reporter: Bravery is rewarded here. I choose this guy. Reporter: And daniel was going to need all his courage. The survival rates from this kind of cancer -- they're very low. Reporter: How low for someone his age? 12 years old. And he low. I just can't even bring myself to say. Reporter: How low? Survival is not very common. Reporter: But the doctors here have a way of beating the odds. There is no time to waste. How do you feel? Good. Reporter: Doctors need to know immediately if the surgeons in upstate new york were able to remove the entire time in daniel's brain or whether cancer cells are still spreading. Almost my height. Reporter: Dr. Bakazy will SUPERVISE A SERIES OF MRIs TO Find out. We are monitoring his blood pressure, his heart rate, his oxygen, his breathing closely from the control room while he's having a scan. At the same time he's listening to the shrek music, he's relaxed, he's comfy. &#9834; I thought love was only true in fairy tales &#9834; Reporter: The next day daniel and lisa meet radiation oncologist dr. Larry kahn. Daniel is nervous, worried about the test results. Yeah, actually today's scans look good. Really? Reporter: But dr. Kahn is unaware that he and his mother have not yet been told the RESULTS OF THE MRIs. His spinal looks okay. Okay meaning there's nothing -- oh, I'm so excited. That's awesome. I guess you didn't know that. It looks good. I actually stayed up late at night actually researching everything they said about the spines because you've got to take action immediately. The spine just connects to all the organs and everything. That's true. And your spine looks perfectly good. Oh, I'm so happy. Get your butt over here. Reporter: Daniel will not just receive treatment at st. Jude -- that's all somewhat preliminary. Reporter: He's part of a research protocol, as are all the children admitted to the hospital. Octopus. He's on a protocol, probably the most intense in the nation, for this type of tumor. Reporter: But as rigorous as THE TREATMENT IS, THEin St. Jude's does its best to let the sick kids here still be kids. And they've arranged a treat especially for daniel. Oh, my gosh. The acrobatic finish on the other end. Reporter: Even the tough guys on the memphis grizzlies respond to daniel's courage. All right. You take care of yourself. All right? You can keep that ball. Thanks. You can have that. Thank you. Mom, I can keep the ball. It was awesome. Words can't explain how happy and grateful I am. Reporter: An experience that will help carry him through the grueling months to come. It's january 2008. Welcome to hogwarts. Reporter: Harry potter fills the room. Daniel's chosen a tape of the young wizard to help him through his radiation therapy. This is his 19th treatment. Daniel, we're going to take a couple of films today. Reporter: The dose must be big enough to stop the cancer from returning while doing as little damage as possible to daniel's brain. Everything's pushing really hard and they have to line up all the lasers. You're not just putting on an act for us? You feel strnong? Mm-hmm. I do. I feel strong like mentally and physically. Reporter: By the end of january daniel has received 31 radiation treatments. And finally, he is allowed to go home to auburn, new york for the month of february. Everyone sewed a little patch for who was praying for me, and I just love it. Reporter: And best of all, daniel has some old-fashioned fun. Oh, I love the snow. I just don't want to hit my incision. Mom made me wear a helmet. Reporter: Of course his friendsrail elated to have him home. Now that he's back I'm really happy. I've been thinking about him a lot. He's -- he's always, you know, in our hearts. We're always thinking about him. When we get home, we're plying the wii. Reporter: The month at home is delicious for daniel. And painful. A reminder of all he is missing. In march it's time for him to return to st. Jude for chemotherapy. Daniel's anxious the. The chemotherapy has been described to him as poisons that are going to be put into his body. And they will kill the good cells as well as the bad cells. Reporter: The chemotherapy will turn out to be even worse than they fear. I was horrified. I wasn't strong. I was in complete disbelief of how sick the kids actually become. Daniel biljanoski. 27163. Reporter: Many days daniel is violently ill. During the course of his chemo he's also being given his own stem cells to help him tolerate the massive doses in a relatively short period of time. Finally, after three months of chemotherapy, by june it has come to an end. I feel so light-headed that i might even trip over my legs. Reporter: It has been seven months since his cancer was diagnosed. And you will be saying good-bye to memphis. But you're going to miss us. Reporter: Finally, a month later in july, after regaining some of his strength, daniel is headed home.

This transcript has been automatically generated and may not be 100% accurate.

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